The present invention relates to a method for calibrating a system for controlling thrust and steering of a drive arrangement in a watercraft, said system comprising an operating device adapted for indicating a requested direction of travel of said watercraft, the operating device being connected to a control unit for providing corresponding thrust and steering commands to said drive arrangement.
The invention also relates to an arrangement for calibrating a system for controlling thrust and steering of a drive arrangement in a watercraft, wherein said system comprises an operating device adapted for indicating a requested direction of travel of said watercraft, the operating device being connected to a control unit for providing corresponding thrust and steering commands to said drive arrangement.
When controlling a watercraft, for example in the form of smaller ships and leisure boats, there is a general need for arrangements which allow a precise control of the thrust and steering of the watercraft. In particular, there is a need for a arrangements providing accurate control of the watercraft during docking. In this regard, the term “docking” refers to a manoeuvre in which a watercraft is propelled towards a harbour, marina or pier in order to be landed and secured.
In certain situations, the docking manoeuvre can be quite difficult for the driver of the watercraft, for example when the watercraft must be landed with one of its sides towards the harbour, for example in a space between two other boats. Such a situation can be simplified if the watercraft is arranged to be propelled in the sideways direction, i.e. in a direction which is generally transverse to the longitudinal direction of the watercraft.
Such a sideways movement of a watercraft can be carried out if the watercraft is provided with two drive arrangements which are separately controllable, i.e. independently of each other. The drive arrangements can for example be in the form of conventional combustion engines which are connected to propellers. By shifting one of the engines into reverse and operating the other engine in forwards drive, while at the same time carefully adjusting the steering angles of the two propellers, the watercraft can be brought to move in a direction which is essentially transverse to its longitudinal direction.
A similar type of docking manoeuvre can also be obtained in watercraft provided with bow thrusters or stern thrusters. A bow thruster comprises a propeller which is mounted in the bow, generally transverse to the longitudinal direction of the watercraft, in order to generate a side force on the bow. In this manner, the watercraft can be more easily controlled when docking or maneuvering at low speeds. A similar arrangement, a so-called stern thruster, can be provided in the stern of a watercraft.
The patent document U.S. Pat. No. 4,519,335 discloses a device for controlling the direction of movement of a watercraft by separately controlling two steerable propellers. For example, the watercraft can be given a thrust in a lateral direction.
However, a docking manoeuvre requires a careful control of the steering and thrust of the engines. It should also be noted that the movements of a watercraft during docking are, to a large extent, determined by the position of the centre of rotation of the watercraft. The centre of rotation is an imaginary point which can be calculated for each watercraft and which defines a vertical axis about which the watercraft may rotate. The fact that the centre of rotation may vary for a certain watercraft means that a control command for steering the watercraft in a certain direction may not always correspond exactly to the direction of the operating device on which the control command is carried out. This problem is further emphasized through the fact that the efficiency for a twin-engine drive arrangement is different in the forwards drive of a propeller as compared with reverse operation.
Consequently, a problem with previously known control systems for watercraft is that they do not allow a steering, for example during docking, in which the movements of a manually operable steering control device correspond precisely to the actual direction of movement of the watercraft. In some cases, a manipulation of a steering control device along a direction which is transverse to the longitudinal direction of the watercraft may in fact lead to a curve-shaped course of travel of the watercraft.
It is desirable to provide a method and arrangement for calibrating an operating device for a watercraft, by means of which the above-mentioned problems can be solved, and which in particular gives an accurate and precise command over the direction of movement of a watercraft.
A method according to an aspect of the present invention comprises the following steps: receiving an activation command in the control unit, for beginning said calibration, detecting any movements of said operating device, storing values corresponding to said movements in the control unit together with corresponding thrust and steering values, and repeating said detecting step and said storing step until a termination command is received in the control unit, thereby using said stored values in subsequent operation of the operating device for indicating said direction of travel of the watercraft.
In an arrangement according to an aspect of the present invention, said control unit is adapted for receiving an activation command from said operating device, indicating a beginning of said calibration, and that said control unit is also adapted for detecting movements of said actuator, for storing values corresponding to said movements in the control unit together with corresponding thrust and steering values, and for repeating said detecting step and said storing step until a termination command is received in the control unit, thereby using said stored values in subsequent operation of the operating device for indicating said direction of travel of the watercraft.
By means of an aspect of the present invention, certain advantages are accomplished. For example, a docking function with the watercraft will be easier to be carried out by its driver, and will be perceived as more accurate. Also, the control unit may control this accurate docking function without having to make complicated calculations as regards the position of the centre of rotation of the watercraft.